Without knowing what reddit is doing, I’m not sure. A JS redirect could be detected, but if OPs paid shortener service is working then reddit is probably working off a simple domain block list. In that case you could use throw away domains.

But JS redirect, proxy response, etc all could just become a game of cat and mouse. Just depends how motivated either side is. But given how big reddit is, i think you’d have the advantage. Just gets expensive since each time your domain gets blocked you’ll be paying to register a new one.